In accordance with a rapid spread of information relevant apparatuses and communication apparatuses such as a personal computer, a video camera and a portable telephone in recent years, the development of a battery to be utilized as a power source thereof has been emphasized. The development of a high-output and high-capacity battery for an electric automobile or a hybrid automobile has been advanced also in the automobile industry. A lithium battery has been presently noticed from the viewpoint of a high energy density among various kinds of batteries.
Liquid electrolyte containing a flammable organic solvent is used for a presently commercialized lithium battery, so that the installation of a safety device for restraining temperature rise during a short circuit and the improvement in structure and material for preventing the short circuit are necessary therefor. On the contrary, a lithium battery all-solidified by replacing the liquid electrolyte with a solid electrolyte layer is conceived to intend the simplification of the safety device and be excellent in production cost and productivity for the reason that the flammable organic solvent is not used in the battery.
A sulfide solid electrolyte material has been known as a solid electrolyte material used for an all solid state lithium battery. For example, in Non Patent Literature 1, an Li ion conductor (a sulfide solid electrolyte material) having a composition of Li4-X)Ge(1-X)PXS4 is disclosed. In addition, it is described in this Literature that Li ion conductance is maximized at x=0.75, and the Li ion conductance is 2.2×10−3 S/cm at a temperature of 25° C. Also, in Patent Literature 1, a solid electrolyte material synthesized from Li2S and a sulfide of one kind or more selected from P2S3, P2S5, SiS2, GeS2, B2S3 and Al2S3 is disclosed.